1. Field of the Invention
The present invention relates to an apparatus and method for plating a substrate, and more particularly to an apparatus and method used for plating metal films on a surface of a substrate such as a semiconductor wafer having fine interconnection grooves, holes or apertures of resist films thereon, or for forming solder bumps or protruding electrodes for electrically connecting to electrodes of semiconductor chip packages.
2. Description of the Related Art
In a TAB (Tape Automated Bonding) process or “flip-chip” process, the surface of a semiconductor chip having interconnects is formed with bumps or protruding electrodes comprised of gold, copper, solder, or nickel, or a layered structure of the above-mentioned materials, for electrically connecting with other chip package electrodes or TAB electrodes.
Such bumps can be formed by processes such as electroplating, vapor deposition, printing, and ball-bumping. Recent trends of increasing numbers in I/O terminals on semiconductor chips and smaller pitches of interconnections have lead to a wide use of electroplating, which can provide fine structure metallization and relatively stable operation.
Electroplating processes can be generally categorized in two types: a fountain type or cup type process in which a substrate such as a semiconductor wafer is plated while the surface to be plated faces downward and a plating solution flows upward to metallize the surface; and a dip type process in which the substrate is vertically placed in a plating vessel (container, cell, or the like) and the solution is supplied from the bottom to overflow from the top of the plating vessel.
FIG. 28 shows an example of a conventional dip type electroplating unit. The electroplating unit comprises: a substrate holder 10 for detachably holding a substrate W such as a semiconductor wafer; a plating vessel 16 containing a plating solution 12 in which the substrate W supported by a substrate holder 10 and an anode 14 are immersed so as to confront each other; and a power source 18 for applying plating voltage between the anode 14 and feeder layer (seed layer) formed on the surface to be plated of the substrate W to supply plating current. An overflow vessel 22 is provided beside the plating vessel 16 for receiving a plating solution 12 which has flowed over an upper edge of an overflow weir 20 of the plating vessel 16. The overflow vessel 22 and the plating vessel 16 are communicated through a circulation line 24 provided with a circulation pump 26, a thermostat unit 28, and a filter 30. Thus, the plating solution 12 driven by the circulation pump 26 is supplied to and fills the plating vessel 16, and then overflows the weir 20 to flow into the overflow vessel 22 and returns to the circulation pump 26 for circulation.
With the plating unit, and by supplying the plating solution 12 into the plating vessel 16 from the bottom portion to overflow the weir 20, arranging the substrate holder 10 in the plating solution 12 within the plating vessel 16 so as to confront the anode 14, and applying prescribed plating voltage between the anode 14 and the substrate W, a plated film is formed on the surface of the substrate W.
A plurality of paddles 34 (agitating rods) are vertically suspended from a lower surface of a paddle shaft 32, which is arranged above the plating vessel 16, horizontally between the substrate holder 10 and the anode 14, and parallel to their surfaces. The paddle are reciprocated horizontally in a direction parallel to the substrate W via the paddle shaft 32 to agitate the plating solution 12 within the plating vessel 16, so as to facilitate the formation of a plating film with uniform thickness.
Also, the substrate holder 10 used in the conventional dip type electroplating unit can detachably hold the substrate W while sealing the peripheral edge surface and the rear surface to expose the front surface to be plated. The substrate W is immersed in the plating solution 12 together with the holder for plating.
It is necessary to securely seal the peripheral portion of the substrate to prevent the plating solution from infiltrating to the rear surface of the substrate, which solution confronts the surface to be plated when the holder is immersed into the plating solution. A conventional substrate holder comprises a pair of supports (holding members) which are open- and closeable to each other, and one support is provided with a fixer ring. The substrate holder is used to hold a substrate by driving the fixer ring to rotate, while the substrate is held between the supports, to push the one support toward the other so that the a seal ring attached to the one support is pressed against the peripheral region of the substrate surface for sealing.
When the substrate is subjected to a series of steps including plating and other accompanying processes, the substrate is held by the holder and the holder having the substrate is transferred to plating or processing vessels, and the substrate is immersed into the plating solution or other processing solutions together with the holder.